Patch and sensor assembly for use in medical device localization and mapping systems

ABSTRACT

An patch and sensor assembly for use in an EP mapping system has two portions: a reusable portion and a disposable portion. The reusable portion houses the biosensors used in magnetic based location and mapping systems and the electrical lead necessary to communicate between the biosensor and the mapping system. The reusable portion may also contain a portion of the electrode necessary to receive electrical signals from the body of the patient. The disposable portion of the patch and sensor assembly contains an adhesive covered flexible patch having at least a portion of the electrode used to receive electrical signals form the body of the patient and may contain the electrical lead necessary to communicate such an electrical signal to the mapping system. The disposable portion contains a receptacle adapted to receive and mechanically secure the reusable portion to the disposable portion of the assembly. Such a patch and sensor assembly is useful in hybrid magnetic and impedance based location and mapping systems such as those used in electrophysiology.

FIELD OF THE INVENTION

The present invention relates to mechanisms for the attaching a reusablecable and housing containing a biosensor for magnetic field basedlocalization to a conductive and adhesive patch assembly having at leasta portion of an electrode used for electrical and mechanical contactwith the body surface of a patient. More particularly, the inventionrelates to a patch and cable attachment mechanism optimized for use inan electrophysiology mapping and ablation system using both biosensorsand electrodes for magnetic and impedance or current based localizationand mapping of medical devices in the human body.

BACKGROUND OF THE INVENTION

Many abnormal medical conditions in humans and other mammals have beenassociated with disease and other aberrations along the lining or wallsthat define several different body spaces. In order to treat suchabnormal conditions of the body spaces, medical device technologiesadapted for delivering various therapies to the body spaces using theleast invasive means possible.

As used herein, the term “body space,” including derivatives thereof, isintended to mean any cavity within the body which is defined at least inpart by a tissue wall. For example, the cardiac chambers, the uterus,the regions of the gastrointestinal tract, and the arterial or venousvessels are all considered illustrative examples of body spaces withinthe intended meaning.

The term “vessel,” including derivatives thereof, is herein intended tomean any body space which is circumscribed along a length by a tubulartissue wall and which terminates at each of two ends in at least oneopening that communicates externally of the body space. For example, thelarge and small intestines, the vas deferens, the trachea, and thefallopian tubes are all illustrative examples of vessels within theintended meaning. Blood vessels are also herein considered vessels,including regions of the vascular tree between their branch points. Moreparticularly, the pulmonary veins are vessels within the intendedmeaning, including the region of the pulmonary veins between thebranched portions of their ostia along a left ventricle wall, althoughthe wall tissue defining the ostia typically presents uniquely taperedlumenal shapes.

One means of treating body spaces in a minimally invasive manner isthrough the use of catheters to reach internal organs and vessels withina body space. Electrode or electrophysiology (EP) catheters have been incommon use in medical practice for many years. They are used tostimulate and map electrical activity in the heart and to ablate sitesof aberrant electrical activity. In use, the electrode catheter isinserted into a major vein or artery, e.g., the femoral artery, and thenguided into the chamber of the heart that is of concern in order toperform mapping and ablation procedures. It is important to know and beable to map the location of the tip or other portions of such electrodecatheters within the vessels or other locations in the body space.

U.S. Pat. Nos. 5,391,199, 5,443,489, 6,788,967 and 6,690,963 toBen-Haim, whose disclosures are incorporated herein by reference,describe systems wherein the coordinates of an intrabody probe aredetermined using one or more field sensors, such as a Hall effectdevice, coils, or other antennae carried on the probe. Such systems areused for generating three-dimensional location information regarding amedical probe or catheter. Preferably, a sensor coil is placed in thecatheter and generates signals in response to externally appliedmagnetic fields. The magnetic fields are generated by three radiatorcoils, fixed to an external reference frame in known, mutually spacedlocations. The amplitudes of the signals generated in response to eachof the radiator coil fields are detected and used to compute thelocation of the sensor coil. Each radiator coil is preferably driven bydriver circuitry to generate a field at a known frequency, distinct fromthat of other radiator coils, so that the signals generated by thesensor coil may be separated by frequency into components correspondingto the different radiator coils.

In United States Patent Application No. 2007/0016007 filed by Govari andincorporated herein by reference, a hybrid position sensing systemincludes a probe adapted to be introduced into a body cavity of asubject. The probe includes a biosensor having a magnetic fieldtransducer and at least one probe electrodes. A control unit isconfigured to measure position coordinates of the probe using themagnetic field transducer of the biosensor. The control unit alsomeasures an impedance between the at least one probe electrodes and oneor more points on a body surface of the subject. Using the measuredposition coordinates, the control unit calibrates the measuredimpedance.

Thus, in such a hybrid magnetic and impedance based systems, a biosensorand electrode must be placed at multiple points on the boy surface ofthe patient. Because the biosensors and the electrical cablingconnecting them to the EP mapping system are relatively expensive, it isideal that the biosensors and the associated cable be reusable. Theportion attached to the skin is preferably disposable, therefore, adisposable patch is necessary for affixing the reusable biosensor andpossibly a portion of the electrode to the skin of the patient.

Existing patches comprises one or more stainless steel studs, foam and aconductive adhesive gel that is in contact with the skin of the patient.The matching patch cable in existing systems primarily comprise one oremore matching stainless steel snaps into which the studs of the patchmate, a biosensor and the associated electrical cable all housed in anepoxy shell. Existing biosensor cable and patch mechanisms areradiopaque, i.e., the stainless steel snaps and studs appear onfluoroscopy. When multiple snaps are used which is often the case inorder to provide a secure and non-rotating connection between the patchand the sensor cable, the multiple snaps do not allow the patch to takethe shape of the body. Also, the patches are often large and conflictwith other patches used on the body for ECG, defibrillators,intra-cardiac echograms, etc.

Prior art mechanisms do not provide an adequate solution. For example,U.S. Pat. No. 3,606,881, relates to a disposable patch having a metallicterminal with an enlarged head which permits a squeeze activated clip tobe secured around the metallic terminal. U.S. Pat. No. 3,829,826provides a mechanical mechanism for attaching to the standard malemetallic snap of the standard ECG patch. U.S. Pat. No. 4,490,005 relatesto a patch in which the central stud is a metal coated non-metallicsubstrate and which permits rotation of the sensor cable while reducingthe effect of rotation on the metal to metal connection. U.S. Pat. No.4,635,642 relates to a disposable pad in which a conductive, preferably,silver coated metallic stud is inserted in order to make electricalconduct with a gel matrix that is in contact with the skin of thepatient.

A similar conductively coated electrically conductive plastic isprovided in U.S. Pat. No. 5,499,628 as an eyelet that is press fit intoa terminal made of a resilient nonmetallic composition such aspolypropylene blended with carbon fiber.

U.S. Pat. No. 5,615,674 relates to a clamping contact connection forcontacting a fetal scalp probe.

U.S. Pat. No. 5,782,761 relates to a molded electrode one-piece and twopiece constructions for a molded electrode made of a conductive materialsuch as a carbon-filled plastic.

U.S. Pat. No. 6,650,922 relates to an electrode element made of anelectrode made of a biodegradable material that is also electroconductive.

U.S. Pat. No. 6,780,065 relates to a device for electrical connection ofthe power lead to an electrode for use on the skin.

U.S. Pat. No. 7,226,299 relates to a circular electrical connector thatengages the socket of a female connector that may include a lockingdevice having resilient prongs.

Design Pat. 240,166 relates to a medical electrode with a rectangularcube portion.

U.S. Patent Application Publication No. 2006/0167354 relates to a systemfor connecting an electrode to a conductive cable.

U.S. Patent Application Publication No. 2006/0149146 relates to a devicehaving an electrode for contact with the patient and a pressure sensor.

U.S. Pat. No. 5,978,693 relates to an electrode having a deformationsensor such as a strain gauge.

It is an object of the present invention to provide a patch that isgenerally not visible under fluoroscopy.

It is a further object of the present invention that the patch becapable of being smaller than currently used patches so as to minimizethe amount of space used on the skin of the patient and reduce potentialconflict with other patches.

Additionally, it is an object of the present invention to provide apatch and sensor cable that will not rotate as would previous designsutilizing a single snap.

Furthermore, it is an object of the present invention to have a patchand sensor cable attachment mechanism that is easy to attach.

Additionally, it is an object of the present invention to have a patchand sensor cable design that could be used for ECG or other instrumentsystems.

Finally, it is an object of the present invention to have a patch andsensor cable attachment mechanism that enables repeated reuse of thebiosensor and sensor cable without any degradation in performance.

SUMMARY OF THE INVENTION

The present invention generally relates to an electrode patch andmagnetic sensor assembly for use in an electrophysiology mapping andablation system. More specifically, the present invention relates to apatch and sensor assembly in which a magnetic-based biosensor is housedin a reusable portion that connects to the mapping and localizationsystem whereas at least a portion of the electrode is in a disposablepatch assembly.

More specifically the present invention discloses a patch and sensorassembly for use in a device mapping system used to map the location ofa device within the body of a patient comprising a reusable portion anda disposable portion. The reusable portion includes a magnetic-basedbiosensor for providing location information about the location of thedevice within the body of the patient to the device mapping system, ahousing adapted to house the biosensor and a first electrical lead forcommunicating an electrical signal from the biosensor to the devicemapping system. The disposable portion comprises an adhesive hydrogellayer for adhering the electrode to the body of the patient, anelectrode layer disposed on the adhesive hydrogel layer, a foam layerdisposed on a portion of the electrode layer; and an engagement elementadapted to detachably receive at least a portion of the housing of thereusable portion.

The reusable portion of the patch and sensor assembly of the presentinvention may also include an electrode element capable of makingelectrical contact with the electrode layer of the disposable portion.This electrode element would then be connected to a second electricallead for communicating an electrical signal from the electrode elementto the device mapping system. The electrode element may be carbon fibercoated on at least one dimension with a conductive metallic materialsuch as is silver chloride. Other materials such as copper, gold,platinum, or silver may also be used as the reusable electrode elementand silver, gold or platinum may also be used as the conductive coating.

Rather than have a conductive cable from the electrode element in thereusable portion, the disposable portion may include second electricallead for communicating an electrical signal to the device mappingsystem.

Alternatively, the disposable portion of the patch and sensor assemblymay have a second electrical lead for communicating an electrical signalto a third electrical lead in the reusable portion wherein said thirdelectrical lead communicates said electrical signal to the devicemapping system.

The foam layer of the patch and sensor assembly may have at least oneindentation adapted to receive the sensor housing and sensor cable.Multiple indentations permit various orientations of the sensor housingand cable.

The sensor housing is comprised of a polymer preferably from the groupconsisting of polyamide, polyurethane, nylon, PEBAX and PEEK polymersand blends thereof.

The reusable portion of the patch and sensor assembly may furthercomprise a strain relief element for reducing mechanical strain on theconnection between the biosensor and the sensor cable.

The disposable portion of the patch and sensor assembly includes one ormore arcuate lips adapted to engage a ridge on the sensor housing of thereusable portion in a snap-fit manner. In an alternate embodiment theengagement element of the disposable portion comprises one or moreflexible engagement members adapted to engage one or more indentationsin the sensor housing.

Alternatively, the reusable portion includes a second engagement elementadapted to engage the engagement element of the disposable portion suchas a mechanical snap.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a planar view of the top of the patch and sensor cableassembly in accordance with a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the patch and sensor cableassembly of FIG. 1 through line A-A.

FIG. 3 is a perspective view of the strain relief element for use inpatch and sensor cable assembly of FIG. 1.

FIG. 4 is a perspective view of a second embodiment of a patch andsensor cable connector in accordance with the present invention.

FIG. 5 is a planar view of the top of a further embodiment of a patchand sensor cable assembly in accordance with the present invention.

FIG. 6 is a cross-sectional view of the embodiment of the patch andsensor cable assembly of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 depicts a planar view of an embodimentof the patch and sensor cable assembly in accordance with the presentinvention. As shown in FIG. 1, the patch and sensor assembly 100comprises two major components: a patch assembly 110 and a sensor cableassembly 130. Sensor cable assembly 130 comprises a sensor housing 122that is adapted to connect to the patch assembly 110 and a sensor cable124. In FIG. 1 the connection between the sensor housing 122 and patchassembly 110 is a snap-fit based on the engagement of ridge 123 ofsensor housing 122 and the lip of engagement element 114 of patchassembly 110. Patch assembly 110 comprises a foam disk 112 having aplurality of indentations 113 adapted to receive the sensor cable 124.The patch assembly in FIG. 1 is shown with three such indentationsenabling a user to attach the sensor cable assembly in one of threepositions even after the disposable patch assembly has been placed onthe patient. One or more such indentations 113 may be used with theupper limit constrained by the ability of the remaining engagementelement 114 to securely engage the ridge 123 of sensor housing 122.Engagement element 114 contains indentations that match those in foamdisk 112. The foam used to form foam disk 112 may be any suitablematerial such as thermofoam, any elastomers like rubbber, santoprene,polyurethane etc. and is preferably thermofoam.

FIG. 2 depicts a partial cross-section of the patch and sensor assemblyof FIG. 1 taken through line A-A. Foam disk 112 rests on a carbon filmdisk 116 coated with a layer of silver chloride on both sides. Carbonfilm disk 116 is approximately 0.5 mm in thickness and the layer ofsilver chloride is approximately 0.1 mm in thickness. Other thicknessesof carbon film disk 116 and silver chloride coating may be used withoutdeparting from the spirit of the invention. On the patient facing sideof carbon film disk 116 is a hydrogel layer 117. Hydrogel layer 117 iscomprised of a conductive gel medium, which also has adhesive propertiesto the skin, preferably a hydrogel being a mix of Silver/Silver Chloridewith water based compound and is approximately 1 mm mm in thickness.

Foam disk 112, carbon film disk 116 and the hydrogel layer 117 generallyhave approximately the same diameter which should be large enough toprovide a secure attachment to the body surface of the patient and ispreferably between 4 cm and 16 cm. The only other component of patchassembly 110 is the engagement element 114. Patch assembly 110 comprisesonly low-cost components in order to increase the disposability of thepatch assembly in this embodiment.

The other component of the patch and sensor assembly 100 depicted inFIGS. 1 and 2 is the reusable sensor cable assembly 130. The reusablesensor cable assembly 130 comprises the aforementioned sensor housing122. Sensor housing 122 is a two-piece design in which upper housingportion 122 a is design to fit together with lower housing portion 122b. Lower housing portion 122 b contains the ridge 123 that engagesengagement element 114 of the patch assembly although this ridge couldbe disposed on the upper housing portion without departing from thespirit of the present invention. Sensor housing 122 is comprised of apolymer such as ABS, nylon, polypropylene or other suitable polymerknown in the art and is preferably made from polypropylene. Sensorhousing 122 could be comprised of more than two parts without departingfrom the spirit of the invention.

Sensor cable assembly 130 further comprises the sensor cable 124 whichcomprises a conductive ACL cable made of a conductive and flexiblematerial, preferably 28 gauge braided copper wire, three twisted pairconductors for the biosensor has along with two Kevlar fibers for addedstrength inside a polymeric outer sheath. One wire in sensor cable 124is welded or bonded using a conductive epoxy to biosensor 126.

Sensor cable assembly 130 further comprises active current location(ACL) disk 134 which may be made of a suitably conductive material andis preferably a generally circular carbon disk coated with silverchloride. Gold or platinum may also be used instead of silver chloridefor the coating and the carbon disk could be replaced with a polymersuch as ABS or polycarbonate with or without carbon fibers embeddedtherein. ACL cable 136 is attached to ACL sensor 134 using a suitableconductive epoxy, preferably any epoxy preferably embedded silverparticles. In use, current flowing through the patient is conductedthrough the hydrogel layer 117, carbon film disk 116 to ACL sensor 134and through ACL cable 136 to the localization and mapping system thatuses the ACL information to perform localization and mapping functionsin accordance with United States Patent Application No. 2007/0016007filed by Govari and incorporated herein by reference or other suchsimilar system.

Sensor cable assembly 130 further comprises biosensor 126 which is abiosensor implemented in accordance with one or more of U.S. Pat. Nos.5,391,199, 5,443,489, 6,788,967 and 6,690,963 to Ben-Haim, whosedisclosures are incorporated herein by reference. Magnetic field basedinformation from biosensor 126 is an electrical current induced by themagnetic field in which the patient is placed and is used in a mannersimilar to that used in the Carto™ EP mapping systems manufactured andsold by Biosense Webster, Inc. The electrical current from biosensor 126is conducted through three twisted pair conductors of the sensor cableassembly 130 to biosensor cable which connects to and EP mapping andlocalization system where the information is used. Biosensor 126 ishoused in biosensor housing 138. Isolation layer 139 is thin piece ofplastic material preferably polypropylene, ABS or polycarbonate whichisolates the 4 KV defibrillation pulse from ACL wire to the biosensor126.

As can be seen from FIGS. 1 and 2, it is advantageous to have thebiosensor 126, ACL sensor 114 and the sensor cable 124 in the reusablesensor cable assembly 130 in order to reduce the cost of the disposablepatch assembly 110. The sensor cable assembly 130 is connected to thepatch assembly using an easy to operate snap-fit connection. This forcewill hold the re-usable to the disposable part. The sensor cableassembly may be positioned in one of several orientations around thecentral axis of the patch assembly but rotation is prohibited by thecombination of the engagement element 114 and the matching indentationsin the foam disk 112.

FIG. 3 depicts a perspective view of the sensor housing 122 showing theupper sensor housing 122 a, the lower sensor housing 122 b and the ridge123. Sensor assembly 122 preferably includes the strain relief element125 but may also be substantial circular without such element. Strainrelief element 125 may be integral with sensor housing 122 or maycomprise a separate polymeric sleeve that covers a portion of sensorcable 124.

FIG. 4 depicts a perspective view of a further embodiment of a patch andsensor cable connector in accordance with the present invention. Sensorhousing 222 has a plurality of indentations 223 which are adapted toengage under flexible engagement members 215 which form a portion ofengagement element 214. As in the previous embodiment described above,sensor housing 222 forms a part of a sensor cable assembly 230 andengagement element 214 form a part of the patch assembly 110. Engagementelement 214 is made from a polymer that is sufficiently flexible toenable flexible engagement members 215 to be pushed toward the peripherywhile the sensor cable assembly 230 is inserted into the engagementelement 214. The snap of re-usebable to disposable part is held using acantilever beam tab. The disposable part will have the lever whichdeflects during the snapping operation. The normal forces exherted fromthe cantilever beam hold the snap together

FIGS. 5 and 6 depict a planar top view and cross sectional view ofanother embodiment of a patch and sensor assembly in accordance with thepresent invention. Patch and sensor assembly 300 comprises two portions:a patch cable assembly 310 and a sensor cable assembly 330. Patch cableassembly 310 comprises a foam disk 312 having indentation 313 (withportions 313 a and 313 b) to accommodate the sensor housing 322 andengagement element 314. Two separate cables are used to connect thebiosensor and ACL sensor to the mapping and localization system. ACLcable 334 is used to connect the ACL sensor layer 316 to the system fortransmittal of current information to the localization system.Alternatively, the ACL cable 334 can be substantially shorter than thelength necessary to reach to the mapping and localization system and canbe adapted to have a fitting that is designed to connect to a matedfitting on a cable that is collinear with the sensor cable. In theconfiguration, the fitting on the ACL cable is attached to the fittingon the additional cable that forms part of the sensor cable. In thismanner, a substantial length of the ACL cable becomes part of thereusable sensor cable assembly. ACL cable 334 is stranded 28 gauge wirethat is sandwiched between the foam disk 312 and the ACL sensor layer316. ACL sensor layer 316 is a silver chloride coated carbon film ofapproximately 1 mm with a silver chloride coating of approximately 0.5mm. Below the ACL sensor layer 316 is a hydrogel layer 317 substantiallythe same as the one described above with respect to the otherembodiment.

FIG. 5 has the snap feature in the form of three legs. This feature alsoworks similar to principle of cantilever beam of FIG. 4. The legsdeflect on the reusable part conforming to the opening on the disposableside. When snapped the beam expands providing the normal force to holdthe two parts together.

Sensor cable assembly 330 comprises the engagement element 314, sensorhousing 322 with biosensor 326 mounted inside. Sensor cable 324 is usedto connect the biosensor 326 that provides magnetic based localizationinformation to the system. Sensor cable 324 is a 48 gauge braided copperwire coated with a protective polymer with an exposed end welded orbonded, preferably using a conductive epoxy to the biosensor 326. Strainrelief element 325 covers a portion of the sensor cable 324 in order toreduce mechanical stress on the connection of the sensor cable to thebiosensor and sensor housing. Biosensor 326 is substantially similar tobiosensor 126 for the embodiment described above. Engagement element 314is a mechanical snap designed to engage patch cable assembly 310.Engagement element 314 has moveable elements 314 a and 314 b that aredepressed in order to release and/or engage the engagement element ontothe patch assembly.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes in the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention.

Accordingly, the foregoing description should not be read as pertainingonly to the precise structures described and illustrated in theaccompanying drawings, but rather should be read consistent with and assupport to the following claims which are to have their fullest and fairscope.

What is claimed is:
 1. A patch and sensor assembly for use with a devicemapping system capable of mapping a relative location of a device withinthe body of a patient comprising: a reusable portion and a separatedisposable portion, the reusable portion comprising: a magnetic-basedbiosensor configured to generate magnetic field based locationinformation signals in response to externally applied magnetic fieldsfrom at least one magnetic field generator fixed to an externalreference frame, and to provide the magnetic field based locationinformation signals to the device mapping system, wherein the magneticfield based location information is indicative of the relative positionof the patch and sensor assembly within the external reference frame; ahousing adapted to house the biosensor; a first electrical lead forcommunicating the magnetic field based information signals from thebiosensor to the device mapping system; and, the separate disposableportion comprising: an adhesive hydrogel layer for adhering thedisposable portion to the body of the patient; an electrode layerdisposed on the adhesive hydrogel layer, the adhesive hydrogel layer andthe electrode layer being part of a first electrode element, wherein thefirst electrode element is configured to conduct and communicate animpedance-based electrical signal directly to the device mapping system,the impedance-based electrical signal is the result of energy flowingthrough the body of the patient from an interbody-electrode on thedevice to the first electrode element and is indicative of the locationthe device within the body relative to the patch and sensor assembly; afoam layer disposed on a portion of the electrode layer; and, anengagement element adapted to detachably receive at least a portion ofthe housing of the reusable portion.
 2. The patch and sensor assembly ofclaim 1 wherein the reusable portion further comprises a secondelectrode element capable of making electrical contact with the firstelectrode element of the disposable portion.
 3. The patch and sensorassembly of claim 2 wherein the reusable portion further comprises asecond electrical lead for communicating an electrical signal from thesecond electrode element to the device mapping system.
 4. The patch andsensor assembly of claim 2 wherein the second electrode elementcomprises carbon fiber coated on at least one dimension with a metallicmaterial.
 5. The patch and sensor assembly of claim 4 wherein themetallic material is silver chloride.
 6. The patch and sensor assemblyof claim 4 wherein the metallic material is selected from the groupconsisting of: silver chloride, gold and platinum.
 7. The patch andsensor assembly of claim 1 wherein the disposable portion furthercomprises a second electrical lead for communicating an electricalsignal to the device mapping system.
 8. The patch and sensor assembly ofclaim 1 wherein the disposable portion further comprises a secondelectrical lead for communicating an electrical signal to a thirdelectrical lead in the reusable portion wherein said third electricallead communicates said electrical signal to the device mapping system.9. The patch and sensor assembly of claim 1 wherein the foam layercomprises at least one indentation adapted to receive the biosensorhousing and the first electrical lead.
 10. The patch and sensor assemblyof claim 1 wherein the sensor housing is comprised of a polymer.
 11. Thepatch and sensor assembly of claim 10 wherein the polymer is selectedfrom the group consisting of polyamide, polyurethane, nylon, PEBAX andPEEK polymers and blends thereof.
 12. The patch and sensor assembly ofclaim 1 wherein the foam layer is comprised of thermofoam.
 13. The patchand sensor assembly of claim 1 wherein the reusable portion furthercomprises a strain relief element for reducing mechanical strain on theconnection between the biosensor and the sensor cable.
 14. The patch andsensor assembly of claim 1 wherein the engagement element of thedisposable portion comprises one or more arcuate lips adapted to engagea ridge on the sensor housing of the reusable portion in a snap-fitmanner.
 15. The patch and sensor assembly of claim 1 wherein theengagement element of the disposable portion comprises one or moreflexible engagement members adapted to engage one or more indentationsin the sensor housing.
 16. The patch and sensor assembly of claim 1wherein the reusable portion comprises a second engagement elementadapted to engage the engagement element of the disposable portion. 17.The patch and sensor assembly of claim 16 wherein the second engagementelement is a mechanical snap.